"""DISCONTINUED"". The Lung Cancer Biology Section has undertaken two prospective trials to study the role of ectopic production of arginine vasopressin and atrial natriuretic peptide in 64 patients with lung cancer. These studies were undertaken to define the impact of these hormones on sodium homeostasis as well as the renin, angiotensin, and aldosterone system. Fifty patients, 31 with small cell lung cancer and 19 with non-small cell lung cancer participated in the initial clinical trial. Eleven patients presented with hyponatremia; 10 patients with small cell lung cancer (32%) and 1 patient with non-small cell lung cancer. All 11 patients who presented with hyponatremia had inappropriately elevated levels of AVP. Elevated plasma AVP levels were highly correlated with the presence of hyponatremia (p"